1. Field of the Invention
This invention pertains generally to integrated circuits, and more particularly to constant voltage generators.
2. Description of Related Art
A constant voltage generator (Vref generator) is widely used within many Integrated Circuit (IC) designs, such as voltage references, input buffers, voltage regulator circuits, and similar applications. Typically the most crucial requirement for a Vref generator is that of providing a constant output voltage regardless of operating voltage, ambient temperatures, operating temperatures and manufacturing process variations. Various BandGap References (BGR) which rely on the use of diodes or bipolar transistors (P-N junction potential) have been utilized for this purpose. Recently, however, CMOS Vref generators have drawn increasing attention because of their simple design, low power consumption, and their ability to be readily incorporated on-chip within a wealth of CMOS circuit designs.
FIG. 1 depicts a conventional CMOS Vref generator having a single input and output stage. The Vref output is generated through PMOS device MP2 from drop R1 in combination with active resistor MP1 and R2 forming a voltage divider with active circuits MN1 and MN2. However, conventional CMOS Vref generators exhibit substantial operating voltage and temperature variations which makes them unsuitable for use in a number of important applications.
Accordingly, a need exists for a system and method of generating an accurate voltage reference from simple CMOS circuitry while overcoming the problems with process variations, supply voltage changes, and temperature drift. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed voltage generator systems and methods.